RU2324001C1 - Method of thearmal treatment and chemical-thearmal method of steel products processing in vacuum - Google Patents

Abstract

FIELD: production methods.

SUBSTANCE: it is made the azotization and bright hardener by vacuum heating in plasma of heighten density, formed between the product and screen by creating the effect of full cathode. The plasma of heighten density is formed from mixture with the following ratio, mass %: azoth 50-80, argon 10-25, acetylene 10-25. The azotization is produced under the temperature 700-850°C. the bright hardener is realized by heating from the temperature of azotization up to 900-1100°C, holding during 15-30 min and sudden cooling in the stream of helium, which exceeds the critical temperature of steel hardiness. Then it is done the deep drawing under 250-350°C.

EFFECT: it is increased the contact longevity and durability of harden layer.

1 ex, 1 dwg

Description

The invention relates to the field of thermal and chemical-thermal treatment and can be used in mechanical engineering and other industries for surface hardening of machine parts and cutting tools from structurally alloyed and tool steels operating at high contact stresses and under conditions of increased wear.

The known method (RU 2058421 C1, IPC С23С 8/36. 04/20/96) nitriding of parts from structural alloy steels, including high-temperature ion nitriding, quenching from the temperature of complete dissolution of nitride phases, tempering, machining and low-temperature ion nitriding to a depth of not less than depths of the de-nitrated layer.

The disadvantage of the analogue is the complexity of equipment and technology, as well as the need to design special equipment.

The known method (RU 2127330 C1, IPC C23C 8/26. 10.03.99) heat treatment to form a high-strength austenitic surface layer in stainless steels, including nitriding in a nitrogen-containing gas atmosphere at 1000-1200 ° C and subsequent cooling at a speed that avoids nitride precipitation.

The disadvantage of the analogue is the complexity of equipment and technology, as well as the need to design special equipment.

The closest in technical essence and the achieved effect to the claimed one is the method (RU 2276201 C1, IPC C23C 8/36, C21D 9/30. 11/09/2004) processing of steel products, including nitriding in a glow discharge, for the implementation of which vacuum heating of the products in high density nitrogen plasma formed between the part and the screen due to the creation of a hollow cathode effect.

The disadvantages of the prototype are:

- a high probability of decarburization of the surface, which can lead to a sharp increase in the fragility of the nitrided layer and its peeling due to the absence of carbon-containing gases in the saturating medium;

- low cooling rate by argon flow due to the low heat capacity of this gas, which can lead to incomplete hardening or the formation of a ferrite-cementite mixture;

- lack of tempering - as a mandatory operation for steel products hardened to martensite, for complete stress relief.

It should also be noted that immediately after quenching in the zone of high nitrogen content (1.5-2.0%), the γ phase that has not undergone martensitic transformation is retained, which leads to a decrease in the hardness of this zone. To obtain a fully martensitic structure (tempered martensite), tempering is necessary at a temperature of 250 ÷ 300 ° C.

The problem to which the invention is directed is to increase the productivity of the nitriding and light hardening process, increase the contact durability and wear resistance of the hardened layer, as well as expand the functionality of this method due to high temperature nitriding, surface hardening and subsequent tempering in one technological cycle.

The problem is solved by using a method of processing steel products, including nitriding and light hardening by vacuum heating in a plasma of increased density formed between the product and the screen by creating a hollow cathode effect, and in contrast to the prototype, a plasma of increased density is formed from a mixture containing nitrogen, argon and acetylene in the following ratio, wt.%:

nitrogen - 50 ... 80,

argon - 10 ... 25,

acetylene - 10 ... 25,

while nitriding is carried out at temperatures of 700 ÷ 850 ° C, and light hardening is carried out by heating from nitriding temperature to 900 ÷ 1100 ° C, holding for 15-30 minutes and quenching in a helium stream at a speed exceeding the critical rate of steel quenching, after which carry out low tempering at 250 ÷ 350 ° C.

The hollow cathode effect is manifested in a significant increase in current density, an increase in the degree of plasma ionization, while reducing the discharge burning voltage.

The invention is illustrated by the drawing, which shows a diagram of the implementation of the method of high-temperature nitriding of products in a glow discharge with the effect of a hollow cathode. The circuit includes a power source 1, anode 2, cathode-part 3, a screen in the form of a grid 4, mounted at a certain distance from the cathode-part 3, a gas supply device for cooling 5.

An example of a specific implementation of the method.

The method is as follows: in the vacuum chamber, the workpiece is installed, for example, a bearing cage made of alloyed structural steel SHX15, and a screen. Then, a working pressure equal to 100 Pa is created in the chamber, which is necessary for ignition of a glow discharge. A mixture of gases (N ₂ 50% -80%, Ar 10% -25%, C ₂ H ₂ 10% -25%) is fed into the chamber. Using the hollow cathode effect, the part is heated to a temperature of 700 ÷ 720 ° С - pre-conversion of the ferrite-cementite mixture into austenite, while high-temperature nitriding takes place for 1-3 hours, then light-quenched heating is performed from the nitriding temperature to 900 ÷ 1100 ° C, holding for 15–30 min and rapid cooling in a helium stream at a rate of V _cool. = 300 deg / s, providing the martensite structure within a given section of the product. Immediately after quenching, tempering is carried out at a temperature of 250 ÷ 300 ° C.

All processes take place in one technological cycle, in one chamber and in one atmosphere. Using this method will reduce the auxiliary time spent on preparatory operations, which are associated with the use of different equipment and accessories.

Nitriding, combined with hardening and tempering, will provide high hardness, endurance, contact fatigue resistance, wear resistance and corrosion resistance. This processing method will significantly increase the durability of parts and cutting tools.

Using the hollow cathode effect will ensure uniform heating of the surface of the part to the required temperature, increase the thermal efficiency of heating, and reduce energy consumption.

It should be noted the following advantages of the claimed method: high technological process, the possibility of heat treatment in the absence of expensive protective or hardening media (various oils, salt solutions), environmental cleanliness of the process due to the absence of harmful industrial emissions into the atmosphere, the ability to control processing parameters in a wide range of modes from heating to active melting, and due to this - structure, hardness, wear resistance, roughness, lack of hardening defects, as well as ease of processing circuit, which does not require special equipment design, and relatively low cost equipment.

Claims (1)

A method of processing steel products, including nitriding and light hardening by vacuum heating in a plasma of increased density formed between the product and the screen by creating a hollow cathode effect, characterized in that the plasma of increased density is formed from a mixture containing nitrogen, argon and acetylene in the following ratio components, wt.%: nitrogen 50-80 argon 10-25 acetylene 10-25 while nitriding is carried out at temperatures of 700-850 ° C, and light hardening is carried out by heating from nitriding temperature to 900-1100 ° C, holding for 15-30 minutes and quenching in a helium stream at a speed exceeding the critical rate of steel quenching, after which carry out low tempering at 250-350 ° C.